The prior art describes various measuring devices serving the purpose of examining any desired materials optically. Such measuring devices are used, inter alia, in agriculture in order to classify harvest material, and in the food industry for the purpose of characterizing and monitoring raw materials. Measuring devices based on spectroscopic methods and/or on an optical detection of the samples (with the use of image processing systems) have been described:
DE 199 22 867 A and DE 10 2004 048 103 A describe spectroscopic measuring devices for agricultural harvesting machines which comprise a light source which radiates the sample, in particular harvest material, with a light during operation. Light reflected by the sample is deflected in a spectrometer in different directions dependent on wavelength by a dispersive element for example a grating or a prism. Detector elements receive the light, which is now assigned to known wavelengths and whose wavelengths lie in the visible wavelength region or in the near infrared region. The output signals of the detector elements are fed to an evaluation device which calculates specific parameters of the sample with the aid of the measured spectra.
Measuring devices which are based on an optical detection of the samples and use image processing systems have been described in U.S. Pat. No. 6,119,442 A, WO 2006/010761 A and EP 1 671 530 A. The sample is irradiated with light and the reflected light is detected by a camera. In accordance with U.S. Pat. No. 6,119,442 A, for example, after an image analysis by means of the image processing system information is available relating to the brokens content in the threshed grain of a combine harvester after passage through the threshing device, and/or relating to the fraction of the impurities in the cleaned grain after passage of the cleaning device, and is used for the automatic setting of the concave gap and/or the speed of the cleaning fan. In the case of a forage harvester, EP 1 671 530 A proposes to illuminate the chopped harvest material with a flash light and to examine it with a camera in order to evaluate the actual cut length.
DE 20 2005 001 438 U, which is regarded as generic, describes a measuring arrangement having a near infrared spectrometer and a camera which detects light indirectly reflected by the sample and which light originates from an incandescent lamp. The spectrometer and the camera are arranged inside a common housing and cooperate with the sample through a window. The combined evaluation of the data records of the spectrometer and of the image data records on the camera is intended to improve the accuracy of the measurements of the spectrometer for example in the spectroscopic measurement of the mineral content of flour while considering the appearance, the colour and the existing blackenings of the flour which are detected by the camera.
The sample is illuminated in DE 20 2005 001 438 U by a light source in the form of a halogen lamp. The light from the light source is used jointly by the camera and the spectrometer. Because of different wavelengths required by the spectrometer (near infrared region) and the camera (visible light), a very wideband light source is required which has a poor efficiency. Again, optimizing the light source for the wavelengths of the spectrometer or the camera would entail a worsening of the illumination in the wavelengths of the other sensor element. Furthermore, the light source operates continuously in the prior art, the result of this being that the camera requires a very short shutter speed in order to record relatively quickly moving samples sufficiently sharply.
Thus, there is a need for providing a measuring device that provides improved illumination of the sample.